Image Credit: Siemens Water Technologies
Clarifiers and screens are used to remove solids from liquids through gravity settling or a mechanical screening process. They are used to treat wastewater and purify drinking water.
Types of Clarifiers
The GlobalSpec SpecSearch database defines clarifier types by technology and categorizes individual products as conventional, sludge blanket, and suction type. Suppliers, however, may describe products by application, shape, or configuration.
Conventional clarifiers are gravity sedimentation tanks (settlers) whose primary end product is a clarified liquid. They are available in rectangular and circular configurations.
Sludge Blanket Clarifiers
Sludge-blanket clarifiers are up-flow products, meaning that water flows upward from the bottom of the clarifier through a blanket of suspended solids that acts as a filter. These clarifiers contain an inverted cone that produces an increasing cross-sectional area from the bottom to the top. The upward velocity or the water decreases at it nears the top.
The upward velocity of the water balances the downward velocity of the solid particle, and the particle becomes suspended. The heavier particles are suspended more closely to the bottom while the lighter ones are suspended more closely to the surface. As the water containing flocculated solids passes upwards through this blanket, the particles are absorbed onto the larger floc, which increases the floc size and drops to a lower level. Eventually, it falls to the bottom of the clarifier to be recirculated or drawn off.
Suction type clarifiers use a vacuum system to collect the sludge from the bottom of the tank. They are used for secondary and final clarification processes. There are two basic designs. The most common is a circular device with bottom-mounted vacuum tubes. The other type is a traveling bridge device.
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